The long range objective of this research is to use neurophysiological and psychophysical techniques to develop a better understanding of pain perception. In this grant we propose to continue studies of peripheral neural mechanisms of pain sensation. Chronic pain often results from injury to the peripheral nerve, and thus results of these studies may have direct relevance to the treatment of chronic pain. An important strategy of this research is to correlate the response of primary nociceptive afferents, obtained from single fiber recordings in the monkey, with the response of human subjects, based on ratings of subjective magnitude, when both are exposed to the same stimuli. The specific goals are: (1) to characterize further the normal response properties of primary nociceptive afferents in order to understand better the peripheral neural coding mechanisms for thermal and mechanical pain perception, (2) to continue research on the neural mechanisms of primary and secondary hyperalgesia induced by cutaneous injury and antidromic nerve stimulation, (3) to initiate studies of the response properties of nociceptive afferents following peripheral nerve injury, and (4) to determine the effects of electrical stimulation of the peripheral nerve on the responses of primary nociceptive afferents.